netdev - Re: [PATCH] [RFC] net: phy: Fix reboot crash if CONFIG_IP

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Date:   Mon, 4 Jan 2021 18:43:42 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] net: phy: Fix reboot crash if CONFIG_IP_PNP is not
 set

On Mon, Jan 04, 2021 at 06:31:05PM +0100, Andrew Lunn wrote:
> > The basic rules here should be, if the MDIO bus is registered, it is
> > usable. There are things like PHY statistics, HWMON temperature
> > sensors, etc, DSA switches, all which have a life cycle separate to
> > the interface being up.
> 
> [Goes and looks at the code]
> 
> Yes, this is runtime PM which is broken.
> 
> sh_mdio_init() needs to wrap the mdp->mii_bus->read and
> mdp->mii_bus->write calls with calls to
> 
> pm_runtime_get_sync(&mdp->pdev->dev);
> 
> and
> 
> pm_runtime_put_sync(&mdp->pdev->dev);
> 

Agree. Thanks for actually looking into it.. I'm not really well versed
in runtime PM.

> The KSZ8041RNLI supports statistics, which ethtool --phy-stats can
> read, and these will also going to cause problems.
> 

Not really, this driver connects to the PHY on .ndo_open(), thus any
try to actually dump the PHY statistics before an ifconfig up would get
an -EOPNOTSUPP since the dev->phydev is not yet populated.

This is exactly why I do not understand why some drivers insist on
calling of_phy_connect() and its variants on .ndo_open() and not while
probing the device - you can access the debug stats only if the
interface was started.